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Soil Water Storage (soil + water_storage)
Selected AbstractsModelling variable source area dynamics in a CEAP watershedECOHYDROLOGY, Issue 3 2009Helen E. Dahlke Abstract In the Northeast US, saturation excess is the most dominant runoff process and locations of runoff source areas, typically called variable source areas (VSAs), are determined by the available soil water storage and the landscape topographic position. To predict runoff generated from VSAs some water quality models use the Soil Conservation Service Curve Number equation (SCS-CN), which assumes a constant initial abstraction of rainfall is retained by the watershed prior to the beginning of runoff. We apply a VSA interpretation of the SCS-CN runoff equation that allows the initial abstraction to vary with antecedent moisture conditions. We couple this modified SCS-CN approach with a semi-distributed water balance model to predict runoff, and distribute predictions using a soil topographic index for the Town Brook watershed in the Catskill Mountains of New York State. The accuracy of predicted VSA extents using both the original and the modified SCS-CN equation were evaluated for 14 rainfall-runoff events through a comparison with average water table depths measured at 33 locations in Town Brook from March,September 2004. The modified SCS-CN equation captured VSA dynamics more accurately than the original equation. However, during events with high antecedent rainfall VSA dynamics were still under-predicted suggesting that VSA runoff is not captured solely by knowledge of the soil water deficit. Considering the importance of correctly predicting runoff generation and pollutant source areas in the landscape, the results of this study demonstrate the feasibility of integrating VSA hydrology into water quality models to reduce non-point source pollution. Copyright © 2009 John Wiley & Sons, Ltd. [source] Apparent/spurious multifractality of data sampled from fractional Brownian/Lévy motionsHYDROLOGICAL PROCESSES, Issue 15 2010Shlomo P. Neuman Abstract Many earth and environmental variables appear to be self-affine (monofractal) or multifractal with spatial (or temporal) increments having exceedance probability tails that decay as powers of , , where 1 < , , 2. The literature considers self-affine and multifractal modes of scaling to be fundamentally different, the first arising from additive and the second from multiplicative random fields or processes. We demonstrate theoretically that data having finite support, sampled across a finite domain from one or several realizations of an additive Gaussian field constituting fractional Brownian motion (fBm) characterized by , = 2, give rise to positive square (or absolute) increments which behave as if the field was multifractal when in fact it is monofractal. Sampling such data from additive fractional Lévy motions (fLm) with 1 < , < 2 causes them to exhibit spurious multifractality. Deviations from apparent multifractal behaviour at small and large lags are due to nonzero data support and finite domain size, unrelated to noise or undersampling (the causes cited for such deviations in the literature). Our analysis is based on a formal decomposition of anisotropic fLm (fBm when , = 2) into a continuous hierarchy of statistically independent and homogeneous random fields, or modes, which captures the above behaviour in terms of only E + 3 parameters where E is Euclidean dimension. Although the decomposition is consistent with a hydrologic rationale proposed by Neuman (2003), its mathematical validity is independent of such a rationale. Our results suggest that it may be worth checking how closely would variables considered in the literature to be multifractal (e.g. experimental and simulated turbulent velocities, some simulated porous flow velocities, landscape elevations, rain intensities, river network area and width functions, river flow series, soil water storage and physical properties) fit the simpler monofractal model considered in this paper (such an effort would require paying close attention to the support and sampling window scales of the data). Parsimony would suggest associating variables found to fit both models equally well with the latter. Copyright © 2010 John Wiley & Sons, Ltd. [source] Spatial patterns of simulated transpiration response to climate variability in a snow dominated mountain ecosystemHYDROLOGICAL PROCESSES, Issue 18 2008Lindsey Christensen Abstract Transpiration is an important component of soil water storage and stream-flow and is linked with ecosystem productivity, species distribution, and ecosystem health. In mountain environments, complex topography creates heterogeneity in key controls on transpiration as well as logistical challenges for collecting representative measurements. In these settings, ecosystem models can be used to account for variation in space and time of the dominant controls on transpiration and provide estimates of transpiration patterns and their sensitivity to climate variability and change. The Regional Hydro-Ecological Simulation System (RHESSys) model was used to assess elevational differences in sensitivity of transpiration rates to the spatiotemporal variability of climate variables across the Upper Merced River watershed, Yosemite Valley, California, USA. At the basin scale, predicted annual transpiration was lowest in driest and wettest years, and greatest in moderate precipitation years (R2 = 0·32 and 0·29, based on polynomial regression of maximum snow depth and annual precipitation, respectively). At finer spatial scales, responsiveness of transpiration rates to climate differed along an elevational gradient. Low elevations (1200,1800 m) showed little interannual variation in transpiration due to topographically controlled high soil moistures along the river corridor. Annual conifer stand transpiration at intermediate elevations (1800,2150 m) responded more strongly to precipitation, resulting in a unimodal relationship between transpiration and precipitation where highest transpiration occurred during moderate precipitation levels, regardless of annual air temperatures. Higher elevations (2150,2600 m) maintained this trend, but air temperature sensitivities were greater. At these elevations, snowfall provides enough moisture for growth, and increased temperatures influenced transpiration. Transpiration at the highest elevations (2600,4000 m) showed strong sensitivity to air temperature, little sensitivity to precipitation. Model results suggest elevational differences in vegetation water use and sensitivity to climate were significant and will likely play a key role in controlling responses and vulnerability of Sierra Nevada ecosystems to climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source] Soil water repellency in a Japanese cypress plantation restricts increases in soil water storage during rainfall eventsHYDROLOGICAL PROCESSES, Issue 17 2007Masahiro Kobayashi Abstract Forest soils in Japan are often water repellent. Substantial water repellency frequently occurs and impedes water infiltration into the soil matrix, but continuous overland flow is not necessarily observed because forest soils usually have macropores through which the water can enter the subsoil. Although this flow pattern may influence the manner of water storage in forest soils at the solum scale, field evidence has not yet indicated this process. We monitored soil water storage during natural rainfall events in a 60-cm deep solum using time domain reflectometry (TDR) moisture sensors, and observed stained flow patterns in the soil following simulated rainfall containing a colour dye, on a slope planted with Japanese cypress (Chamaecyparis obtusa). The surface soil at the research plot exhibited strong water repellency at water contents lower than the threshold critical water content of 0·29 m3 m,3. Under dry antecedent moisture conditions, increases in soil water storage were small compared to the cumulative rainfall, despite the low wetness of the soil matrix. In contrast, under moderate moisture conditions, increases in the water content corresponded to the cumulative rainfall. Under dry conditions, rainwater may have entered the subsoil at a few limited locations connected with continuous vertical macropores, such as decayed root channels or interstructural voids. Therefore, the water seemed to bypass a large part of the soil matrix away from the macropores. Such preferential water flow was confirmed by the stained flow patterns after the rainfall simulation. The flow patterns visualized by the dye were discontinuous and scattered under dry conditions and diffuse under moderate moisture conditions. Repellency induced preferential flow led to restricted increases in solum scale water storage during rainfall events, reflecting a physical nonequilibrium in soil water storage. Copyright © 2007 John Wiley & Sons, Ltd. [source] Multi-variable and multi-site calibration and validation of SWAT in a large mountainous catchment with high spatial variabilityHYDROLOGICAL PROCESSES, Issue 5 2006Wenzhi Cao Abstract Many methods developed for calibration and validation of physically based distributed hydrological models are time consuming and computationally intensive. Only a small set of input parameters can be optimized, and the optimization often results in unrealistic values. In this study we adopted a multi-variable and multi-site approach to calibration and validation of the Soil Water Assessment Tool (SWAT) model for the Motueka catchment, making use of extensive field measurements. Not only were a number of hydrological processes (model components) in a catchment evaluated, but also a number of subcatchments were used in the calibration. The internal variables used were PET, annual water yield, daily streamflow, baseflow, and soil moisture. The study was conducted using an 11-year historical flow record (1990,2000); 1990,94 was used for calibration and 1995,2000 for validation. SWAT generally predicted well the PET, water yield and daily streamflow. The predicted daily streamflow matched the observed values, with a Nash,Sutcliffe coefficient of 0·78 during calibration and 0·72 during validation. However, values for subcatchments ranged from 0·31 to 0·67 during calibration, and 0·36 to 0·52 during validation. The predicted soil moisture remained wet compared with the measurement. About 50% of the extra soil water storage predicted by the model can be ascribed to overprediction of precipitation; the remaining 50% discrepancy was likely to be a result of poor representation of soil properties. Hydrological compensations in the modelling results are derived from water balances in the various pathways and storage (evaporation, streamflow, surface runoff, soil moisture and groundwater) and the contributions to streamflow from different geographic areas (hill slopes, variable source areas, sub-basins, and subcatchments). The use of an integrated multi-variable and multi-site method improved the model calibration and validation and highlighted the areas and hydrological processes requiring greater calibration effort. Copyright © 2005 John Wiley & Sons, Ltd. [source] Controls on runoff from a partially harvested aspen-forested headwater catchment, Boreal Plain, CanadaHYDROLOGICAL PROCESSES, Issue 1 2005K. J. Devito Abstract The water balance and runoff regime of a 55 ha aspen-forested headwater catchment located on the Boreal Plain, Alberta, Canada (55·1°N, 113·8°W) were determined for 5 years following a partial timber harvest. Variability in precipitation provided the opportunity to contrast catchment water balances in relatively dry (<350 mm year,1), wet (>500 mm year,1), and average precipitation years. In most years, the catchment water balance was dominated by soil water storage, evapotranspiration losses, and vertical recharge. In 1997, despite near-average annual precipitation (486 mm), there was significant runoff (250 mm year,1) with a runoff coefficient of 52%. A wet summer and autumn in the preceding year (1996) and large snow accumulation in the spring (1997) reduced the soil water storage potential, and large runoff occurred in response to a substantial July rainfall event. Maps of the surface saturated areas indicated that runoff was generated from the uplands, ephemeral draws, and valley-bottom wetlands. Following 1997, evapotranspiration exceeded precipitation and large soil water storage potentials developed, resulting in a reduction in surface runoff to 11 mm in 1998, and <2 mm in 1999,2001. During this time, the uplands were hydrologically disconnected from ephemeral draws and valley-bottom wetlands. Interannual variability was influenced by the degree of saturation and connectivity of ephemeral draws and valley wetlands. Variability in runoff from tributaries within the catchment was influenced by the soil water storage capacity as defined by the depth to the confining layer. An analysis of the regional water balance over the past 30 years indicated that the potential to exceed upland soil water storage capacity, to connect uplands to low-lying areas, and to generate significant runoff may only occur about once every 20 years. The spatial and temporal variability of soil water storage capacity in relation to evaporation and precipitation deficits complicates interpretation of forest harvesting studies, and low runoff responses may mask the impacts of harvesting of aspen headwater areas on surface runoff in subhumid climates of the Boreal Plain. Copyright © 2005 John Wiley & Sons, Ltd. [source] The simulation of heat and water exchange at the land,atmosphere interface for the boreal grassland by the land-surface model SWAPHYDROLOGICAL PROCESSES, Issue 10 2002Yeugeniy M. Gusev Abstract The major goal of this paper is to evaluate the ability of the physically based land surface model SWAP to reproduce heat and water exchange processes that occur in mid-latitude boreal grassland regions characterized by a clear seasonal course of hydrometeorological conditions, deep snow cover, seasonally frozen soil, as well as seasonally mobile and shallow water table depth. A unique set of hydrometeorological data measured over 18 years (1966,83) at the Usadievskiy catchment (grassland) situated in the central part of Valdai Hills (Russia) provides an opportunity to validate the model. To perform such validation in a proper way, SWAP is modified to take into account a shallow water table depth. The new model differs from its previous version mainly in the parameterization of water transfer in a soil column; besides that, it includes soil water,groundwater interaction. A brief description of the new version of SWAP and the results of its validation are presented. Simulations of snow density, snow depth, snow water equivalent, daily snow surface temperature, daily evaporation from snow cover, water yield of snow cover, water table depth, depth of soil freezing and thawing, soil water storage in two layers, daily surface and total runoff from the catchment, and monthly evaporation from the catchment are validated against observations on a long-term basis. The root-mean-square errors (RMSEs) of simulations of soil water storage in the layers of 0,50 cm and 0,100 cm are equal to 16 mm and 24 mm respectively; the relative RMSE of simulated annual total runoff is 16%; the RMSE of daily snow surface temperature is 2·9 °C (the temperature varies from 0 to ,46 °C); the RMSE of maximum snow water equivalent (whose value averaged over 18 years is equal to 147 mm) is 32 mm. Analysis of the results of validation shows that the new version of the model SWAP reproduces the heat and water exchange processes occurring in mid-latitude boreal grassland reasonably well. Copyright © 2002 John Wiley & Sons, Ltd. [source] Soil frost effects on soil water and runoff dynamics along a boreal forest transect: 1.HYDROLOGICAL PROCESSES, Issue 6 2001Field investigations Abstract To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic-rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995,96) had abnormally low snow precipitation, which gave a deep frost down to 40,80 cm, whereas the two following winters had frost depths of 5,20 cm. During winter 1995,96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5,7 vol.% in the mineral soil and 10,15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage. Copyright © 2001 John Wiley & Sons, Ltd. [source] Modification of growing-season surface temperature records in the northern great plains due to land-use transformation: verification of modelling results and implication for global climate changeINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2004Rezaul Mahmood Abstract Land-use and land-cover change can modify near-surface atmospheric condition. Mesoscale modelling studies have shown that modification in land use affects near-surface soil moisture storage and energy balance. Such a study in the Great Plains showed that changes in land use from natural grass to irrigated agriculture enhanced soil water storage in the root zone and increased latent energy flux. This increase in latent energy flux would correspond to a decrease in sensible heat flux and, therefore, modify near-surface temperature records. To verify this deduction, we have investigated the changes in the historical near-surface temperature records in Nebraska, USA. We have analysed the long-term mean monthly maximum, minimum, and monthly mean air temperature data from five irrigated and five non-irrigated sites. The cooperative weather observation (coop) network is the source of the data. We have found that there is a clear trend in decreasing mean maximum and average temperature data for irrigated sites. For example, York, NE, reports that the mean maximum growing season temperature is decreasing at the rate ,0.01°C year,1. The results from non-irrigated sites indicated an increasing trend for the same parameters. The data from Halsey, NE, indicate a +0.01°C year,1 increase in this century. In addition, we have conducted similar analyses of temperature data for the National Climatic Data Center's Historical Climatic Network data set for the same locations. The results are similar to that obtained with the coop data set. Further investigation of dew-point temperature records for irrigated and non-irrigated sites also show an increasing and decreasing trend respectively. Therefore, we conclude that the land-use change in the Great Plains has modified near-surface temperature records. Copyright © 2004 Royal Meteorological Society [source] | ||||||||||